1. Field of the Invention
This invention relates to the chemical-mechanical-polishing (CMP) of flat surfaces and, more particularly, to such polishing of silicon wafers to achieve global planarization in the manufacture of integrated circuits.
2. Description of the Related Art
As is well known and understood, the traditional technique for polishing silicon wafers flat across the entire surface is through the use of circular motion in which a polishing pad and the wafer below it rotate together. As is also known to those skilled in the art, whether the polishing is done purely mechanically, or combined with a liquid affording a chemical function, the typical pad life (because of wear and tear) extends from about 100 wafers to about 500 wafers. Independent of the manner by which the deterioration is measured or determined, there then follows a "down-time" for the changing of the pad, and for the conditioning of its replacement to bring it to the state at which the polish rate is constant. When considering the $40.00-$50.00 cost of each pad as used in polishing silicon wafers of some 8 inches in diameter--and the time spent in replacing and conditioning the pad--calculations have shown that these rotatable pads account for anywhere between 15 and 30 percent of the cost associated with the CMP tool. Because of the necessity to replace, and then condition these pads, a manner of extending the interval between their exchange would be highly desirable.